Revert &quotImplement timers by posting delayed tasks&quot

      This reverts commit 334040f6e54d29d7890b6f409354cd234b29c24b.

Reason: Breaks GN test:

http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_gn_rel/builds/93666/steps/html_viewer_unittests%20%28with%20patch%29/logs/stdio

These tests are only built on GN bots, which absent on Blink canary waterfall.

BUG=463143,416362,480522
TBR=jochen@chromium.org,kinuko@chromium.org,skyostil@chromium.org

Review URL: https://codereview.chromium.org/1162753003

git-svn-id: svn://svn.chromium.org/blink/trunk@196169 bbb929c8-8fbe-4397-9dbb-9b2b20218538